Touch panel devices that can be operated by an operator directly touching a screen while images are displayed on the screen are commonly known. Such touch panel devices are often used in a portable information processing terminals such as a PDAs (Personal Digital Assistants), cellular phone terminals, Smartphones, or the like (hereafter called “electronic devices”). A touch panel device has a touch panel to detect an object approaching the surface. Types of touch panels include a resistor film method that detects resistor value changes to a touched portion, a capacitance type that detects capacitance changes to the touched portion, an electromagnetic conduction method to detect the position of an body with the electromagnetic energy of an body dedicated to emitting a magnetic field, and so forth. Recently, use of capacitance-type touch panels have increased, particularly in the cellular phone terminal and Smartphone markets.
When touch sensitive mobile phones and PDA's were first introduced the main input device was a pen. This changed when Smartphones were introduced where all input was made with your fingers. With finger input, capacitive touch sensors replaced other technologies (like resistive sensors used for pen input) due to increased finger touch sensitivity. Capacitive sensors allowed a lower finger pressure to be detected compared with other technologies.
However, pen input are coming back with recent products. In recent products the capacitive sensors are sometimes complemented, with active pen technology. Active pens allow detection of pen pressure and tilt which cannot be measured directly using capacitive sensors. In these devices, tilt and pressure are e.g. measured by the pen itself and sent to the phone through radio communication.
Typically when drawing on a touch screen, the distance (assume distance of pen tip from surface) is not used, but rather pressure of the pen. Compare with a normal graphite pen. Pressure in current capacitive touch solutions with passive pointers are artificially calculated based on the size of the pointer. A large pointer size is interpreted as much pressure and a small pointer is interpreted as little pressure. When fingers are used as input means it is actually possible to measure pressure indirectly. When the finger is pressed harder against the surface, the size of the contact surface, will increase which is detected by the sensor. There are touchpens designed with a relatively large and soft pen tip (like a finger) which allow pen pressure to be measured in the same way. But when a pen is used for drawing or writing a small pen tip is preferred to allow better visual feedback during drawing.
The sensitivity of capacitive sensors are also being improved which allow almost any kind of passive pen to be used as input device, as long as it is conductive. As an example an ordinary graphite pen with a tip area of at least 1-2 mm may be used with current state of the art technology, but then pen pressure or tilt cannot be measured. Graphite is stiff and can not change footprint which makes it difficult or even impossible to measure preassure with this technology.